Insulator



Nov. 17, 1936. E. D. TREANOR ET AL INSULATOR Filed May 31, 1935 m am uJ E @T U P R & U0 WN A nma B E an Ud b Patented Nov. 17, 1936 UNITED STATES PATENT OFFICE INSULATOR Application May 31,

4 Claims.

Our invention relates to insulators. An insulator is usually secured to a grounded support and carries an electrical conductor which it insulates and spaces from the support. The insulator must provide enough insulation between its support and the conductor so that the normal operating voltage of the conductor will not cause a fiashover of the insulator and, on the other hand, an insulator is often proportioned to flashover under abnormal voltage conditions so as to afford more or less protection to apparatus to which the conductor may be connected. In order that the insulator may flashover and prevent unduly high abnormal voltages on the conductor, an insulator of the usual construction would sometimes have to be undesirably small. If an insulator is too small, flashovers are apt to be caused even under normal voltage conditions by birds or small animals which may come too close to the insulator. Even the appearance of an insulator which is too small is under some conditions not pleasing. There is also not apt to be so much trouble from flashovers due to dust and dirt which may collect on the surface of an insulator which is larger than is necessary for the normal voltage of a conductor carried by it.

The general object of the invention is to provide an improved insulator structure which is largely self-protecting against normal voltage flashovers due to the causes which have been explained.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Fig. 1 is a view of an insulator constructed in accordance with the invention, the insulator being shown partly in section. Fig. 2 is a view of the insulator mounted on the casing of an electrical apparatus such as a transformer. Like reference characters indicate similar parts in both figures. of the drawing,

The invention will be explained as embodied in the insulating bushing II], shown in Fig. 2, in connection with a transformer casing II and shown on a larger scale in Fig. 1. The bushing I0 is of the usual tubular form and secured through the cover I2 of the casing I I and formed with an internal opening for a conductor I3 which may be one of the leads from the transformer in the casing II. The bushing I0 is provided at its outer end with a metal cap I4 carrying a terminal I5 for the lead of conductor I3. The bushing I0 is formed of any suitable insulating material, such as porcelain, and the portion of the bushing I0 outside of the casing II is formed 1935, Serial No. 24,166

with the usual petticoats I6 and H to protect at least part of its surface from the weather and to increase the external surface leakage path between the terminal I5 and the cover I2 of the casing which is usually grounded.

An internal opening is is provided through the base of the petticoat E6 of the bushing so that this opening I8 terminates at its upper end near the terminal cap I l and at its lower end under the petticoat HS and is therefore inside a part of the outer surface of the insulator between the cap i l and the grounded cover I2 of the casing II. An electrode 59 extends from the terminal cap i i into the internal opening I8 so that the lower end of this electrode is considerably closer to the grounded. cover I2 than is the cap I4. The electrode I9 is therefore electrically connected through the cap I4 to the terminal l5 and the conductor IS. The length of this electrode I9 is so proportioned that the external surface leakage path between the lower end of the electrode i9 and the grounded cover I2 will break down or flashover at a. voltage sufficiently low to protect the apparatus in the casing II. This protected gap between the electrode Ill and the cover I2 of the casing II is afforded a considerable degree of protection by the petticoat I I from birds and small animals which might otherwise cause accidental arcing under normal voltage conditions across this gap. The provision of the electrode is also permits the bushing Ill to be as large as desired to present a pleasing appearance in connection with the casing II upon which it is mounted. A length of the gap between the electrode i9 and the cover 12 of the casing I I depends upon the length of the electrode I9 and any degree of protection desired may be secured by selecting an electrode of the proper length.

The invention has been explained by describing and illustrating a particular form and application of the invention, but it will be apparent that changes may be made without departing from the spirit of the invention and the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States, is,-

1. An insulator mounted on a grounded support, a conductor carried by said insulator, said insulator having a petticoat with an opening through its base between said conductor and support, and an electrode within said opening to reduce the external breakdown gap between the conductor and ground.

2. An insulator mounted on a grounded support, a conductor carried by said insulator, said insulator having a petticoa't with an opening through its base between said conductor and support, and an electrode electrically connected to said conductor and extending into said opening to reduce the external breakdown gap between the conductor and support.

3. An insulating bushing secured through an opening in an electrical apparatus casing, a conductor extending through said bushing and having a terminal at the outer end of the bushing, said bushing having an internal opening terminating at one end near said terminal and at the other end at the outer surface of the bushing between said terminal and casing, and an electrode electrically connected to said terminal and extending into said opening to reduce the external breakdown gap between the terminal and casing.

4. An insulating bushing secured through an opening in an electrical apparatus casing, a conductor extending through said bushing and having a terminal at the outer end of the bushing, said bushing having a petticoat with an opening through its base between said terminal and casing, and an electrode electrically connected to said terminal and extending into said opening to reduce the external breakdown gap between the terminal and casing.

EDWARD D. TREANOR. HARRY M. ACLY. 

